Article No. 1141, Ingenieurs de l'Automobile No. 6 1982, pp. 69-77, and in particular FIG. 19 on page 74, describes a safety device for vehicle occupants. The safety device includes squibs, (i.e. firing pellets), which are actuated by a control unit. Upon actuation, the squibs activate a gas-producing propellant charge, which is operatively connected to an internal restraining device for vehicle occupants, such as, in particular, an airbag, and inflate said airbag. U.S. Pat. No. 3,911,391 describes a method for testing such squibs. In this context, the squibs to be tested receive a testing current supplied by a testing current source. The ensuing voltage drop is compared in a comparative circuit to the voltage supplied by a reference voltage source. The accuracy of such measurement is a function of the accuracy of the test current fed to the squib during the test. However, when working with integrated circuits, it is relatively difficult and expensive to provide a highly precise current source.